1. Field of the Invention
The present invention relates to a motor equipped with a motor housing, a brush provided in the motor housing, and a brush holding frame holding the brush.
2. Description of the Related Art
A conventionally known motor for an engine starter is equipped with a motor housing, a stator fixed in position on an inner side of the motor housing, a rotor rotatably provided on an inner side of the stator, a commutator provided on a rotation shaft of the rotor and rotating together with the rotor, a brush one end portion of which is brought into contact with the commutator and the other end portion of which is connected to a lead wire, and an insulating brush holding frame fixed in position on the inner side of the motor housing and holding the brush (see, for example, JP 2829182 B).
The brush is constituted by a positive-pole-side brush connected to a positive-pole-side lead wire and a negative-pole-side brush connected to a negative-pole-side lead wire. The brush holding frame has a positive-pole-side brush holding portion holding the positive-pole-side brush within and a negative-pole-side brush holding portion holding the negative-pole-side brush within. The positive-pole-side brush holding portion is formed in substantially the same thickness as the negative-pole-side brush holding portion, and insulates the positive-pole-side brush from the motor housing.
In this conventional motor, however, the commutator attains high temperature through energization for a long period of time. When the strength of the commutator deteriorates and the rotating commutator undergoes radial outward deformation, the commutator collides with the brush holding frame, resulting in deformation of the positive-pole-side brush holding portion and of the negative-pole-side brush holding portion. In particular, when the positive-pole-side brush holding portion is deformed, the positive-pole-side brush sticks out of the positive-pole-side brush holding portion, so there is a fear of short-circuiting between the positive-pole-side brush and the motor housing.